Roller cone bits are widely used in oil and gas, mining and engineering drilling applications. During drilling, heel row cutters on cones of the bit undertake multiple jobs including break bottom hole rocks by impact actions, gouge borehole wall and help to maintain bit diameter in order to prevent bit diameter shrinkage. Breaking bottom hole rocks by impact actions requires sharper top surface of the insert; gouging borehole wall and maintaining bit diameter require larger contact area between heel row cutter and borehole wall. Heel row cutters normally used on roller cone bits of prior art include inserts with deflected wedge surfaces and conical spherical inserts, which can not meet the two requirements mentioned above simultaneously. Inserts with deflected wedge surfaces has a larger contact area with borehole wall and is helpful for gouging borehole wall and maintaining bit diameter. But this insert has a blunter top surface because there is a plain on the top surface of the insert, and so it is not beneficial to breaking bottom hole rocks by impact actions. When inserts with deflected wedge surfaces are used as heel row cutters on roller cone bit, heel row cutters become one of the main causes to the low rate of penetration. Although conical spherical insert has a sharper top surface and helpful for breaking bottom hole rocks by impact actions, the contact area between heel row cutters and borehole wall become smaller when conical spherical inserts are used as heel row cutters on bit, therefore causing weaker gouging actions to borehole wall and lower gage protection ability of the bit.